Proponents of the death penalty often argue that the threat of being executed acts as a deterrent that prevents people from committing murder. But those who oppose capital punishment challenge that claim. And some researchers argue that state-sanctioned execution might actually increase homicide rates.
Now, a panel of independent experts convened by the prestigious National Research Council has taken a look at this question and decided that the available research offers no useful information for policymakers.
"We recognize that this conclusion may be controversial to some, but nobody is well-served by unsupportable claims about the effect of the death penalty, regardless of whether the claim is that the death penalty deters homicides, has no effect on homicides, or actually increases homicides," says Daniel Nagin, a public policy professor at Carnegie Mellon University who chaired the committee.
This committee did not examine the moral arguments for or against the death penalty. Its job was to look at the science. Nagin says the panel reviewed dozens of studies and found fundamental flaws.
For example, none accounted for the possible effect of other punishments on homicide rates. "The real question is, 'Does the death penalty deter more than other penalties, like life in prison?' None of the research from the past 35 years addresses this problem," says Nagin.
What's more, much of the available research assumes that people who might commit murder can accurately calculate their risk of being executed if they were convicted.
"In reality, this is very difficult to do," says Nagin.
Even researchers have a hard time determining that risk. And, Nagin says, basically nothing is known about how potential murderers — whoever they might be — actually perceive their risk of execution.
The report says it would be possible to design better studies to look at whether the death penalty has a deterrent effect — but they won't be quick or easy.